DE102011018320A1 - Method for regulating the thickness of blown films - Google Patents

Abstract

The invention relates to a method for controlling the film thickness profile of single or multilayer tubular films produced in film blowing systems by detecting the thickness profile of the film tube, subsequent comparison of the detected actual profile with the predetermined nominal profiles, for generating a control variable for influencing the thickness profile of the produced film tube and a device for Implementation of the procedure. The film thickness is influenced so that the final film has a uniform thickness profile and thus also a very good roll quality with high cylindricity. This is achieved in that the control for generating the control variable comprises a cascaded control of a superimposition of a base profile, a roller profile and a scattering profile, wherein the rotation angle and the rotational speed of the turn-up suit or of the blowing head or the winder are smaller than the rotation angle and the Rotation speed that is necessary if the control is not superimposed on a scattering profile

Description

The invention relates to a method for controlling the film thickness profile of single or multilayer tubular films produced in film blowing systems by detecting the thickness profile of the film tube, subsequent comparison of the detected actual profile with the predetermined nominal profiles, for generating a control variable for influencing the thickness profile of the produced film tube and a device for Implementation of the procedure.

The film blowing process is suitable for the production of tubular films. For this purpose, one or more extruder converts plastic granules in plastic melt which is then fed to the blow head. From a ring-shaped nozzle, a molten tube is then drawn. One or more cooling rings cool the melt, resulting in a film tube which is supplied to a flattening, pulled over a reversing turn-off and then wound in a winder. These slides find z. B. Use in the flexible packaging.

State of the art

In the DE 100 47 836 A1 a method for controlling film thickness profiles in blown film is described specifically based on the measurement of one or more individual layer thicknesses of a multilayer film as a controlled variable. The measurement of the film thickness profile over the circumference of the tubular film takes place between Folienblaskopf and flattening. As usual in the prior art, the measured thickness profile is compared with the nominal profile and, in the case of deviations, appropriate control interventions are carried out in the film blowing process. The influencing of the thickness profile is effected by tempering the exiting film tube or the annular nozzle tool. The control is preferably carried out in segments over the circumference of the film tube or the blow head, thereby the thickness profile can be regulated so that the film thickness over the entire circumference of the tubular film is as uniform as possible. The regulation is simple, since there is always a direct assignment of the film to the nozzle or the control zones.

This type of regulation of the film thickness over the circumference of the tubular film is not sufficient for many requirements. Therefore, it has hitherto been necessary, in order to obtain a good roll quality of the wound film, to mechanically displace all the profile points over the roll width via the rotation unit of the turn-off trigger, so that the thin and thick spots of the films on the roll are compensated. This has so far been solved only by means of a complicated mechanical construction of the rotating turn-off trigger or alternatively of the rotating winder or of the rotating blow head. The rotation speed and the rotation angle of the turn-off trigger influence the roll quality. This mechanical displacement has due to the mechanical stress of the film z. B. influence on wrinkling, film defects, sags, surface defects of the film.

The object of the invention is therefore to provide a solution which makes it possible to influence a tubular film produced in a blown film unit with a rotation unit by regulating the film thickness such that the final film has a uniform thickness profile and thus also a very good roll quality with high Cylindricity can be achieved.

The object is achieved by the features in the characterizing part of claim 1.

In a method for controlling the film thickness profile of the type described above, the object is achieved in that the control for generating the controlled variable comprises a cascaded control of a superposition of a base profile, a roller profile and a scattering profile, wherein the rotation angle and the rotational speed of the turn-over suit or of the blowing head or the winder, are smaller than the rotation angle and the rotation speed of the turn-up suit or the blowing head or the winder which are necessary when the control is not superimposed on a scattering profile, so that good roll quality with high cylindricity is achieved.

Description of the invention

In the method according to the invention for controlling the film thickness of tubular films produced in the blown film process, the film thickness profile in the film blowing process is set so that not only does the film have as uniform a thickness profile as possible over its circumference or lying width, but also that a film roll is produced which comprises a film roll Roller profile having the smallest possible deviation in the cylindricity. At the same time, this achieves the effect of minimizing the tendency of the folds, sags, surface defects and film defects of the film caused by the mechanical stress caused by the rotating units.

The film thickness is detected in the region between the film blowing head and flat laying unit over the circumference by means of a measuring device. Alternatively, the film thickness over the width of the lying can be detected when the film thickness in the area after the flattening and before the winder is measured.

In a first control loop, the actual profile is compared with the basic target profile. In the event of deviations, defined control interventions are carried out in the blown film process. As is known from the prior art, film thickness profile control systems are used here. The influence of the thickness profile is z. B. on the segmented control zones in one or more cooling rings by air temperature control or air volume control. Alternatively, the influence of the thickness profile can be done by control zones in the blower head. Here come z. B. heating cartridges used.

In addition, the segmented control zones are assigned the actual profile via an offset, which takes into account the angular offset from the foil swirl. This results from the outlet of the melt from the die, as it is conveyed via so-called spiral distributor in an annular gap to the nozzle.

The tubular film is laid flat after cooling in a trigger and passed over a pair of draw-off rollers. The resulting edges of the film must be assigned to the actuators of the profile control unit. Via a manual or preferably an automatic calibration algorithm, the side edges are assigned to the actuators of the profile control unit. There is an assignment of one or more peripheral points of the flattened in the trigger tube film to one or more of the segmented control zones.

Thus, the given thickness-type polyolefin profile for the film-blowing process can be calculated from the values of the measuring device which measures the thickness profile over the circumference of the film by means of an algorithm.

From the Dickenistprofil, which is detected in the measuring device, the film thickness over the winding width and over the length of the tubular film can be determined and summed up on the roll profile. Upon the emergence of the so-called piston rings on the winding, a control intervention can be made, so that the desired thickness shift over the film width is adjusted. It is compensated for the film thickness change over the width of the film. The basis for this is an assignment of one or more peripheral points of the flattened tubular film ( 6 ) to one or more control zones in the control algorithm for controlling the segmented control zones ( 7 ).

In order to further increase the roll quality and to improve its cylindricity and to further uniform the film thickness over the circumference, another profile is superimposed on the so-called scattering profile. The litter target profile can be calculated manually or by an algorithm and fed to the control system. The scattering profile represents a fixed function (sawtooth profile, sine profile) or a function calculated by an algorithm. It is intended to produce a thick-thin-layer displacement around the circumference of the film, similar to that of a turning bar unit.

Due to the scatter profile control, a part or the complete task of the rotating turn-off deduction can be taken over. The turn-off trigger can be driven with small rotation angles and rotation speeds. There is an optimization between scatter profile control, angle adjustment and rotational speed of the turn-off deduction with respect to the cylindricity of the film roll.

Ideally, the mechanical thick-thin-point displacement is completely replaced by the turn-trigger through the scheme and the rotating turn-off deduction can be omitted.

The control for the control of the individual control zones can be calculated from a superposition of the following thickness profiles via an algorithm. The control zones can be integrated in the blow head, in the cooling ring or in a separate actuator unit.

• – das Grundprofil: welches das Dickenistprofil am Umfang der Schlauchfolie darstellt
• – das Rollenprofil: welches aus dem Dickenristprofil das Dickenprofil der Folienbreite und durch Summation dieser das Rollenprofil hochrechnet, d. h. Rollendurchmesser über Rollenbreite.
• – das Streuprofil: welches eine feste Funktion oder eine durch einen Algorithmus berechnete Funktion darstellt. Es wird dadurch eine Dick-Dünnstellen-Verlagerung ähnlich der aus einer Wendestangeneinheit erzeugt.

The thickness profiles are:

• - The basic profile: which represents the thickness profile on the circumference of the tubular film
• - The roll profile: which extrapolates the thickness profile of the film width from the thickness profile and, by summing this, the roll profile, ie roll diameter over roll width.
• - the scatter profile: which represents a fixed function or a function calculated by an algorithm. It is thereby produced a thick-thin-site displacement similar to that of a turner bar unit.

• – Regelung der Foliendicke über den Schlauchfolienumfang während des Folienblasprozesses
• – Regelung der Wickeldurchmesser über die Wickelbreite
• – Regelung der Dick-Dünnstellen-Verlagerung über die Wickelbreite durch das Streuprofil.

This represents a cascaded control because the following control loops are superimposed:

• - Regulation of the film thickness over the tube film circumference during the film blowing process
• - Regulation of the winding diameter over the winding width
• - Control of the thick-thin-point displacement over the winding width by the scattering profile.

The method for controlling the film thickness is used in systems in which a turning trigger is installed. Here, the Dickensollprofil is changed so that at small setting values of the rotation angle and the rotational speed of the turn-off the result of the film roll with uniform diameter over the winding width without defects caused by mechanical stress. Alternatively, the system can also be used in systems with rotating winder or rotary die.

The film tube can also be supplied block or unbroken to the winders.

The tubular film can be cut as a film tube, one or both sides and fed to the one or more winders.

Further details, features and advantages of the subject matter of the invention will become apparent from the subclaims and from the following description of the accompanying drawings, in which - for example - a preferred embodiment of the invention is shown.

1 : Film blowing plant in which the method according to the invention for controlling the film thickness profiles is used.

The 1 shows a film blowing machine ( 1 ) with foil blowing head ( 5 ), Extraction device ( 8th ), Turn-off ( 9 ) and winder ( 3 ). Via a dosing device ( 2 ), the plastic granulate to be processed is fed to an extruder ( 4 ), in this melted, homogenized and the film blowing head ( 5 ). In the production of multilayer films, several extruders are used according to the number of layers. The foil blowing head ( 5 ) has an annular nozzle from which emerges the extruded plastic mass. Through the film blowing head ( 5 ) is a supply of cooling air to inflate the tubular film ( 6 ). The tubular film ( 6 ) is via the cooling ring ( 7 ) cooled from the outside.

In the cooling ring ( 7 ) is the segmented control zone ( 13 ) arranged. After the plastic has solidified, the tubular film ( 6 ) in the extraction device ( 8th ) laid flat, via a turn-off trigger ( 9 ) and then the winders ( 6 ) and to film winding ( 11 ) rolled up.

The tubular film can be laid flat, blocked or not blocked or after flattening cut on one or both sides of the or the winding points are supplied.

To control the film thickness profile, the detection of the Folienistprofils, preferably at one point is required. The film thickness profile on the circumference of the tubular film ( 6 ) is between Folienblaskopf ( 5 ) and flattening at the measuring device ( 10 ) detected. The measuring device ( 10 ) can alternatively be used between the withdrawal device ( 8th ) and winder ( 3 ), then it captures the film profile across the film width.

About the system control ( 12 ) controls the entire film blowing process, in particular the drives, the cooling air, the segmented control zone located in the cooling ring, in the film blowing head or below. The withdrawal speed of the tubular film is also controlled by the system controller.

That of the measuring device ( 10 ) measured film profile is the plant control ( 12 ) and by a target / actual comparison signals to the segmented control zone ( 13 ).

LIST OF REFERENCE NUMBERS

1

Blown Film

2

metering

3

winders

4

extruder

5

Film die

6

tubular film

7

cooling ring

8th

off device

9

turning deduction

10

measuring device

11

reel

12

system control

13

segmented control zone

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10047836 A1 [0003]

Claims (7)

Method for controlling the film thickness profile of single or multilayer tubular films produced in blown film by detecting the thickness profile of the film tube, then comparing the detected actual profile with the predetermined desired profiles, for generating a controlled variable for influencing the thickness profile of the film tube to be produced characterized in that the scheme for generating the Controlled variable comprises a cascaded control from a superposition of the following profiles: - A basic profile, which controls the thickness of the extruded tubular film over the tube film circumference on a given Dickensollprofils by means of a film thickness profile control system, - a roller profile which captures the film thickness over the winding width summation over the length of the hose and in the occurrence of piston rings on the winding, a control intervention is made so that the desired thickness shift is adjusted over the width of the film, - an S 8, which is a fixed function or a function calculated by an algorithm and produces a thick-thin-film displacement over the film circumference, wherein the rotation angle and the rotation speed of the turn-up suit or the film blowing head or the winder are smaller than the rotation angle and the rotation speed which are necessary if the control is not overlaid with a scattering profile. Method for controlling the film thickness according to claim 1, characterized in that the control for generating the control variable comprises a cascaded control of a superposition of a base profile, a roller profile and a scattering profile, wherein the rotation angle and the rotation speed of the turn-off zero and is omitted. Method for controlling the film thickness according to claim 1, characterized in that the control for generating the control variable comprises a cascaded control of a superposition of a base profile, a roller profile and a scattering profile, wherein the rotation angle and the rotational speed of the film blowing head or the winder are equal to zero. Method for controlling the film thickness according to one or more of the preceding claims, characterized in that an assignment of one or more circumferential points of the flattened tubular film ( 6 ) to one or more control zones in the control algorithm for the segmented control zone ( 7 ) is taken into account. Method for controlling the film thickness according to one or more of the preceding claims, characterized in that the predetermined thickness nominal profile is controlled by an algorithm from the values of a measuring device which measures the film thickness in front of the take-off device in the machine direction over the film circumference. Method for controlling the film thickness according to one or more of the preceding claims, characterized in that the predetermined thickness nominal profile is controlled by an algorithm from the values of a measuring device which measures the film thickness after the take-off device in the machine direction over the entire film width. Device for carrying out the method according to one or more of the preceding claims, characterized in that the device comprises a Folienblasanlage with a film blowing head, a turning trigger, at least one winder and a control system, wherein the control system segmented control zones, preferably a measuring device of the thickness profile of the tubular film after the Folieblaskopf and before the winding station, and a control and evaluation comprises.

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